X-ray apparatus cables for use in explosion hazardous areas



A ril 13, 1965 s. BELL ET AL X-RAY APPARATUS CABLES FOR USE IN EXPLOSION HAZARDOUS AREAS Filed May 1, 1963 ATTORNEY vm oe mm? 25in w oE llllllllllllllllllim 5&3 um? :31 mm N NM ONI\. $55.28 305200 m2] mm mm P nm m. 2 2 t .2 mm mm m United States Patent 3 178,503 X-RAY APPARATI JS CABLES FGR USE TN EXFLOSION HAZARDOUS AREAS Locklin S. Beil and William P. Holland, Miiwaukee, W s,

assignors to General Electric Company, a corporation of New York Filed May 1, 1963, Ser. No. 277,367 2 Claims. (6!. 174-11) This invention relates to X-ray apparatus, and in particular, to a cable assembly for supplying power at high voltage to an X-ray tube in a potentially explosive atmosphere.

X-ray apparatus is often used in explosive atmospheres that are found in industry and hospitals. A typical case is the hospital surgical room where the atmosphere may contain explosive vapors that result from using volatile anesthetics such as ether and cyclopropane and from tinctures of disinfecting agents. If there is a breakdown in the electrical insulation of the X-ray apparatus, there may be sparking which would ignite the vapors and cause an explosion.

The cables which carry electric power from the high voltage supply to the X-ray tube casing are especially susceptible to breakdown because their insulation regularly undergoes flexing and wear as a result of positioning the X-ray tube casing over an object or a patient being subjected to radiography or therapy.

There are two general types of cable used. The first is one that is not intended for use in hazardous atmospheres and it usually comprises conductors that are surrounded with layers of solid but fairly flexible insulation about which there is a concentric braided wire grounding sheath. The grounding sheath may also be covered with flexible insulation and with braided cotton that is covered with protective coatings that meet electrical and mechanical requirements and produce a smooth exterior. If the insulation breaks down, a spark may occur between the grounding sheath and the conductors which is apt to ignite explosive gases, if any are present.

The second type of cable is one that is intended for use in a potentially explosive atmosphere. It may comprise the basic cable described in the preceding paragraph with the addition of a concentric metallic barrier that is filled with an insulating compound like rubber. The outside of the barrier may be covered with further solid but flexible layers to augment the thermal insulating properties and improve appearance. If the insulation between the centrally located conductors breaks down, the heat that is incident to sparking between the conductors and the braided sheath or barrier is confined by or distributed by the barrier so that any surrounding gas is not raised to its ignition temperature which is about 180 C. for ether.

Cables that are wholly insulated with flexible solid materials have several disadvantages. Their flexibility usually suflers at the expense of obtaining dielectric strength and protection against sparking. Moreover, there is no way to anticipate failure. One cannot be certain from inspecting the cable whether its concealed insulating lay ers are fatigued or cracked or subject to failure during the next use. Although an insulation breakdown is likely to cause a protective circuit breaker to open as a result of over current flowing through the low resistance path of the metallic sheating, there is still too much likelihood that a hot spot on the conductors or a spark will ignite the contacting gas and set off an explosion.

The basic object of the present invention is to overcome these disadvantages and to provide X-ray apparatus cables that may be used safely in an explosion hazardous environment.

Additional objects are to provide a cable assembly that surrounds the solid insulation of the conductors with a heat and spark barrier which is in turn enclosed in a flexible tube containing a pressurized insulating gas that excludes the explosive vapors or gases from the region where a fault may occur.

A further object is to provide means for monitoring the explosion preventing capability of the cable by observation of the insulating gas pressure and by disconnecting the apparatus through the agency of a pressure responsive device in the event that there is not adequate pressure dilierential between the inside and outside of the cable to exclude explosive atmospheric gases.

Further specific objects are to provide for X-ray apparatus a cable assembly that is flexible, that is easy to clean and sterilize, that has a pleasing appearance, that is inexpensive and simple to fabricate, and that may be used with most standard X-ray equipment.

Achievement of these and other more specific objects will appear from time to time throughout the course of the ensuing specification.

An illustrative embodiment of the invention employs polyvinyl chloride or other flexible external tube that is sealed at its opposite ends to gas-tight X-ray cable terminations from which electrical connecting prongs extend. A conductor cable inside the tube is loosely surrounded by it. The free space is filled with an insulating gas. The conductor cable is covered with a spiral interlock flexible metal hose that acts as a spark barrier. A metal adapter into which the gas filled tube is sealed, is provided with suitable fittings for filling the tube and for communicating with a pressure gage and a pressure sensitive switch. The switch is adapted to operate de-energizing circuitry of the X-ray apparatus if the gas pressure falls below a predetermined safe minimum value.

A more detailed description of an illustrative embodiment of the invention will now be given in conjunction with the drawings in which:

FIG. 1 shows an X-ray tube casing that is connected to an X-ray power supply and control with the new cable assemblies;

FIG. 2 is a schematic diagram of an X-ray control system in connection with which the new X-ray cables may be used; and

FIG. 3 is a view, partly in section, of the new gas filled X-ray apparatus cable assembly.

In FIG. 1 is shown an X-ray tube casing 10 connected by means of cable assemblies 11 to an X-ray tube power supply and control housing 12. In a typical case, where the housing 12 is admitted to an explosion hazardous area, it will be pressurized with an insulating non-flammable gas such as sulphur hexafluoride, dry nitrogen, Freon 12 or the like. The use of pressurized gas preeludes the explosive atmosphere from coming into contact with sparks that are incident to faults or mere operation of the controls within housing 12. In cases where the X-ray tube power supply and controls are not protected against explosion hazards as they are in this example, it is preferable to keep them outside of the hazardous area and to connect with casing 10 by passing cables 1.1 through the walls of the room which have openings that are above the danger level of six to eight feet for a heavy vapor like ether. In such a case the X-ray tube casing 10 is often pressurized interiorly with insulating liquid in order to prevent admission of explosive gases. The usual mechanism that supports the X-ray tube casing and allows it to be positioned is omitted for the sake of brevity.

In FIG. 1 the exposure factors for the X-ray tube in casing 10 are set by a series of pushbuttons 13-18 that are mounted in the top of gas filled housing 12 and hera vance metically sealed with respect to it. This construction is schematized in FIG. 2 where there is a pushbutton 113 that is accessible to the operator for raising or lowering the voltage on the X-ray tube 14, for instance. Another hermetically sealed pushbutton assembly 15 is used to raise and lower the exposure time setting. Pushbutton 16 may be for controlling the current through the X-ray tube. Also provided is a pushbutton 17, which when depressed, initiates making an X-ray exposure. The apparatus may be energized and de-energized by a line contactor 26 under the control of an on-off pushbutton 18.

The power input to the X-ray tube power supply and control is a three-conductor cable 19 which makes connection with the internal parts of housing 12 through hermetically sealed insulating bushings 2.1. In FIG. 2 the X-ray controls 22 and the X-ray tube power supply 23 are shown in block form because the details of their construction are not necessary to understanding the present invention and they are understood by those versed in the X-ray art. The principal observation to be made in FIG. 2 is that portions of cables 11 pass through the atmosphere to X-ray tube 14 which is in casing in FIG. 1. These cables supply the X-ray tube with voltages, that may be as high as 150 peak kilovolts, and currents in the range of up to 500 milliamperes. Thus, it is seen that the cables are capable of becoming involved in rather high energy faults.

In FIG. 2 there is symbolized a commercial type of pressure responsive switch including a bellows 24 that is hermetically sealed to housing 12 but is exposed to the gas pressure of its interior. If the pressure within housing 12 drops, bellows 24 expands and operates a microswitch 25 which opens line contactor 20 to tie-energize the unit. In this illustrative embodiment of the invention the gas filled cables 11 also communicate with the interior of housing 12 so that if their gas pressure drops, switch 25 will operate to open line contactor 2a.

Housing 12 may be filled with any suitable gas that is preferably both more insulating than atmospheric air and non-combustible. In a commercial form of the X-ray apparatus, the gas in housing 12 is at a pressure of about five pounds per square inch gage and the pressure sensitive switch 24, 25 is adapted to open the line contactor Zti on loss of around two pounds of pressure. A relief valve 26 may be provided for establishing a maximum pressure in housing 12 commensurate with its strength.

The construction of the new cable assembly may be seen best in FIG. 3. It includes a cable 30 which in this case has three conductors with an insulating coating comprising iayers of rubber and semiconductive materials as is conventional. Cable 30 terminates in the cavity 33 'of a male connector body molded of insulating material. Connector body 31 is better known as a standard Federal X-ray cable termination. It is provided with prongs 32 to which the conductors of cable 30 are soldered in a well known manner. The concentric space intervening between the interior wall of body 31 and the cable 30 is filled with an epoxy resin 33 in this case. The resin is preferably of the self-curing type which is admitted through a drill hole, not shown, in the end of the socket adjacent prongs 32. A vent hole is also provided. The resin is admitted in liquid form and cures in place. The surplus fills the vent and filler holes so the body is fluid tight. Materials and procedures for achieving this end need not be described in greater detail since they are well known.

The X-ray apparatus to which the cable assembly connects may be provided with a conventional Federal standard female socket, not shown, which receives the male part 31 to make electrical connection through the agency of prongs 32. The connection is secured by a threaded nut 34 which may screw into an appropriate thread in the mating socket of the X-ray apparatus. Nut 34 may be provided with holes on its left-most face in FIG. 3 to allow engagement with a spanner wrench.

Conductor cable 30 is originally covered with a tinned Wire braid, a short portion of which appears at 35, the remainder being cut off. This braid augments the mechanical strength of the cable and makes it more abrasive resistant besides serving as a spark shield and a convenient ground means. In this instance, braid 35 is electrically connected by soldering to a thin shell 36 constituting a corona cone which is swaged on to a radially projecting shoulder 37 of insulating body 31 as shown. Metallic braid 35 may also be covered with an external fiber braid material which is not exposed in the drawing but which extends over the length of the cable.

Immediately surrounding the cable 30 is a loose fitting spiral wound interlocking flexible metal hose 38 in accordance with the invention. Metal hose 38 serves as an additional heat and spark barrier. It locks when it is bent a predetermined amount so it servesto limit the amount of bending to which the conductor cable 30 may be subjected.

Loosely fitting over metal hose 38 is a flexible outer tubing 39 which may be corrugated metal but which is preferably, as is the case here, made of polyvinyl chloride or other suitable flexible and leak-proof material. The interior of tube 39 is filled with an insulating gas under pressure. To permit this, a suitable sealing arrangement is provided. It involves an adapter 40 that has a radially extending flanged base 41 that is soldered, or fastened by other suitable means, in a leak-proof manher to brass corona shield 36 as shown. Adapter 40 is threaded at one end on its outside to receive the internal thread of a knurled ring nut 42. Nut 42 is internally shouldered to provide a surface for bearing on a bevelled packing ring 43 which squeezes the outside periphery of tubing 39 in a gas-tight manner when nut 42 is tightened by hand. To assure that packing ring 43 is pressed radially inward against a regular surface, there is interposed, between the internal wall of tubing 39 and the outside of flexible metal hose 38, a thin brass ring 44 whose one end is exposed but whose other end extends into tubing 39 at least slightly beyond packing ring 43. The tubing 39 may also be sealed directly to the inside of the cylindrical adapter 46 provided the diameter of the latter is reduced and a suitable adhesive is used.

From the foregoing description it is seen that the interior of adapter 40 forms a cavity 45 that is sealed by packing ring 43 at one end and by the soldered joint effected between flange 41 and corona cone 36 at the other end. There is no opportunity for gas to leak from cavity 45 into bushing body 31 because the latter is filled with a gas impervious resin 33 as described earlier.

When cavity 45 is first evacuated and then filled with insulating gas under pressure, the gas flows into the end of tubing 39 to its interior. There is a slight expansion of tubing 39 when pressurized. Gas also surrounds the periphery of conductor cable 30 which it is able to do by flowing radially through metal hose 38 and inwardly from the end of the metal hose where it is unsealed adjacent Wire braid 35.

To fill cavity 45 and the interior of tubing 39 with pressurized gas, and to establish a path for gas pressure communication with a pressure reservoir, or a gage, or a pressure responsive switch, there is provided a connector 46 that threads into an appropriate opening in the wall of adapter 40. Connector 46 has a gland nut which effects a sealed connection with a nylon or other suitable gas impervious flexible tube 47. The nylon tube is joined with a street elbow 48 by means of a connector 49. Extending from the elbow 43 is a coupling device 69. Coupling 69 is of a type that is commercially available. It is a self-sealing disconnect; that is, when it does not oppose input pressure, a spring biased valve is urged against a seat which effects a seal. Thus, it is possible to pressurize the interior of the cable assembly and to isolate it from the source of gas pressure without losing pressure in the cable assembly. When a connection is made, the valves are urged open so that there is free gas exchange between connected parts.

When it is desired to maintain gas communication between the pressurized cable assembly and a gas reservoir, connector 69 is manually coupled by means of a collar 50 to a mating part which is not shown in FIG. 3. Selfsealing disconnects such as 69 are available from various hardware suppliers. The one here used is a Hansen Connector, Catalog #WB1H11.

The termination of the cable that is remote from the end just described is shown in the left half of FIG. 3. Like parts are assigned the same reference numerals in this portion of the drawing. Modified parts have primed numbers. It will be observed that cavity 45 in the left half of the drawing will receive gas under pressure by flowing through tubing 39 when gas is admitted to the other end of the cable assembly as described above.

' The termination which appears in the left half of FIG. 3 is the one that is admitted to X-ray tube casing in FIG. 1. It will be observed in FIG. 1 that where cable assembly 11 is socketed into casing 10 there is a strain relief 51. This assembly consists of a short piece of interlocking metal hose 52 which terminates in a ferrule at each end, the upper one of which 53 is visible in FIG. 1. In FIG. 3, the ferrule 54 at the end opposite from 53 is admitted to a concentric counterbore in nut 42' circumjacent the pressurized polyvinyl tubing 39. The short metal hose 52 may be secured to the ferrule with epoxy resin. One purpose of the strain relief is to preclude bending the cable assembly 11 too sharply and another is to take the force ofl the cables in the event the operator moves tube casing 10 by gripping the cables instead of the casing itself.

The only other notable modification in the left cable termination in FIG. 3 is that the adapter 40' has no fill connector 46. Of course, the cable ends are interchangeable so as to allow filling and maintaining gas pressure from either end of the cable assembly as a matter of choice.

In the instant example, as illustrated in FIG. 1, the gas in the cable assembly 11 is common with the gas within X-ray power supply housing 12. This results from the fact that nylon tubes 47, which communicate with pressurized interior of cable 11, are connected with the tank through the agency of couplings 49 as described above. Connection is made with housing 12 through a pipe-cross 55 whose bottom branch connects with the housing and whose top branch is provided with a pressure gage 56. The two side branches connect with tubes 47. With this arrangement, gage 56 indicates the pressure that is comfor monitoring both the pressure in the housing 12 and the cable assemblies 11. The latter and housing 12 may be filled jointly with insulating gas through the agency of a self-sealing coupling 57 which communicates through the top of the housing 12.

It is not necessary that the interior of cable assemblies be connected with a pressure reservoir such as housing 12. For example, pipe cross 55 may be removed from housing 12 and the bottom branch of the pipe cross may have screwed into it a pressure sensitive switch assembly such as 24 which is symbolized in FIG. 2. For this arrangement, gage 56 would read the pressure on the cable assemblies 11 independently, that is, without regard to the pressure in any reservoir. Of course, a separate reservoir may be used and the gage may be omitted if desired. The pressure sensitive switch assembly may be adapted to control a circuit that disconnects the power supply in the event pressure is lost in the cable assemblies 11. An arrangement such as this is used in situations where the X-ray tube casing 10 and the cable assemblies 11 are in an explosion hazardous atmosphere but the power supply and other electrical parts are out of it.

Consideration of the way in which the cable assembly is constructed will confirm its multifold advantages. If the layer insulation 30 on the conductors deteriorates or cracks, the dielectric strength of the cable will be restored by virtue of the insulating gas occupying any voids that might be created. If the breakdown is suflicient to cause sparking between the conductors and metal braid 35, for example, the heat incident of sparking encounters a barrier in the form of flexible metal pipe 38 which confines and distributes it and prevents heating of the surrounding explosive atmosphere to a dangerous level. The pressurized non-combustible insulating gas further inhibits sparking and prevents admission of explosive gases to the faulted region. Cables were intentionally faulted in the laboratory while carrying their rated current and voltage but the temperature of the barrier never exceedd C., at which ether ignites Within the time specified for operation of the overload device on the X-ray apparatus. Dual protection is provided. During occurrence of a fault a protective circuit breaker, not shown, will open and isolate it immediately. Concurrently, loss of pressure in the cable assembly causes a pressure sensitive switch 25 to be actuated and it too may open a line contactor such as 20 or other protective device. Moreover, loss of the safe qualities of the cable assembly can be anticipated. The operator may detect leaks by observing a loss of pressure on gage 56, in which case appropriate maintenance procedures may be instituted, and if the loss of gas pressure is unobserved, the pressure sensitive switch 25 will act to prohibit energization of the apparatus. Operating under conditions of maximum safety is thereby assured.

Although one embodiment of the invention has been described in considerable detail, such description is to be considered illustrative rather than limiting, for the invention may be variously embodied and its true spirit and scope are to be determined only by interpreting the claims which follow.

It is claimed:

1. A cable assembly for use with X-ray apparatus in an explosion hazardous area comprising:

(a) an electrical conductor cable having an insulating coating and adapted to transmit power between com ponents of X-ray apparatus,

(b) an insulating body that is sealed to the cable at an end thereof,

(0) said body having sealed terminals extending from it for making connection between the conductor cable and a component of X-ray apparatus,

(d) an external flexible tube means that is gas impervious and surrounds the conductor cable substantially coextensive with its length,

(e) means joining the outside of the flexible tube means and the body in gas tight relation with each other,

(f) a gas pervious flexible barrier means separate from and surrounding said conductor cable in the intervening space between the conductor cable and the inside of the flexible tube means,

(g) means eifecting a gas communication path with the interior of the flexible tube means,

(h) said gas communication path with the interior of the flexible tube including a coupling device connected with the interior of said means that joins the flexible tube and said insulating body,

(i) a pressure responsive switch means that is connected in pressure exchange relation with the pressure inside the tube by way of said coupling device, and

(i) a switch means that is in electric circuit with said pressure responsive switch means and X-ray apparatus and is operable in response to a predetermined drop in pressure on the pressure responsive switch means to de-energize the X-ray apparatus.

2. A cable assembly for use with X-ray apparatus in an explosion hazardous area comprising:

(a) an insulation coated electrical conductor cable for (d) said bushings being filled with an insulating material that encapsulates the cable ends,

( e) a metal shield through which the conductor cable is admit-ted to the respective bushings,

(f) a braided metal covering over the insulated conductor cable that terminates near andis electrically connected to the shield,

(g) a hollow cylinder means sealed to the. shield concentrically about said cable, (h) a spiral Wound interlocking metal hose that is concentric with the conductor cabl'eand extends into-the cylinder means, (i) an outer flexible tubeof non-metallic gas impervious material surrounding said metal hose,

(j) a gasket surrounding said tube,

(k) a nut that is screwed onto the cylinder means to thereby exert component forces that press the gasket against the cylinder means and the tube to make a gas tight seal,

(1) a smooth ring interposed between the inside of the tube and the outside of the metal hose to provide a regular bearing surface for the gasket, and

(m) means elfecting a gas communication path with the interior of the tube.

References Cited by the Examiner UNITED STATES PATENTS 1/ 35- Phillips 174--109 2,222,574 11/ 40 Robertson 174-24 X 2,280,711 4/42 Machlett et a1, 174-75 X 3,037,069 5/62 Wilson 174-89 JOHN F. BURNS, Primary Examiner.

JOHN P. WI-LDMAN, Examiner. 

2. A CABLE ASSEMBLY FOR USE WITH X-RAY APPARATUS IN AN EXPLOSION HAZARDOUS AREA COMPRISING: (A) AN INSULATION COATED ELECTRICAL CONDUCTOR CABLE FOR CARRYING ELECTRIC POWER BETWEEN COMPONENTS OF XRAY APPARATUS, (B) INSULATING BUSHINGS RECEIVING OPPOSITE ENDS OF THE CONDUCTOR CABLE WITHIN THEM, (C) SAID BUSHING HAVING CONDUCTIVE EXTERNAL PRONGS THAT CONNECT WITH THE CONDUCTORS OF THE CABLE INTERIORLY OF THE BUSHINGS, (D) SAID BUSHING BEING FILLED WITH AN INSULATING MATERIAL THAT ENCAPSULATES THE CABLE ENDS, (E) A METAL SHIELD THROUGH WHICH THE CONDUCTOR CABLE IS ADMITTED TO THE RESPECTIVE BUSHINGS, (F) A BRAIDED METAL COVERING OVER THE INSULATED CONDUCTOR CABLE THAT TERMINATES NEAR AND IS ELECTRICALLY CONNECTED TO THE SHIELD, (G) A HOLLOW CYLINDER MEANS SEALED TO THE SHIELD CONCENTRICALLY ABOUT SAID CABLE, (H) A SPIRAL WOUND INTERLOCKING MEATAL HOSE THAT IS CONCENTRIC WITH THE CONDUCTOR CABLE AND EXTENDS INTO THE CYLINDER MEANS, (I) AN OUTER FLEXIBLE TUNE OF NON-METALLIC GAS IMPERVIOUS MATERIAL SURROUNDING SAID METAL HOSE, (J) A GASKET SURROUNDING SAID TUBE, (K) A NUT THAT IS SCREWED ONTO THE CYLINDER MEANS TO THEREBY EXERT COMPONENT FORCES THAT PRESS THE GASKET AGAINST THE CYLINDER MEANS AND THE TUBE TO MAKE A GAS TIGHT SEAL, (L) A SMOOTH RING INTERPOSED BETWEEN THE INSIDE OF THE TUBE AND THE OUTSIDE OF THE METAL HOSE TO PROVIDE A REGULAR BEARING SURFACE FOR THE GASKET, AND (M) MEANS EFFECTING A GAS COMMUNICATION PATH WITH THE INTEROOR OF THE TUBE. 